It is known that synthetic elastomers such as, for example, polybutadiene rubber, polyisoprene rubber, butyl rubber, and styrene-diene rubber, etc., are produced by the catalyzed polymerization of the respective monomers in aromatic or aliphatic organic solvents.
According to known techniques, once the required degree of conversion has been reached, the polymerization reaction is stopped and the solvent is removed from the final solution.
The solvent is generally removed by distillation in a current of steam, producing an elastomer substantially free from organic solvent but containing up to 50-60% water.
In order to eliminate the water from the elastomer, drying is carried out by means of belt dryers which reduce the water content of the elastomer to a value of about 5-10%.
To eliminate the residual water content, the aforementioned drying treatment on belt dryers has to be followed by an extrusion step in suitable extruders which output a substantially anhydrous granulate. The water is eliminated during the extrusion step by virtue of the overheating which occurs because of the friction to which the elastomer is subjected.
The known technique thus produces a solvent- and moisture-free elastomer from the polymerization reaction solution by a method involving three separate steps: distillation in a current of steam, drying and extrusion.
Each of the three steps mentioned above involves the use of apparatus which is generally quite bulky and of considerably complex construction, leading to very high installation and running costs.
Moreover, although the aforementioned extrusion step is effective in eliminating the residual moisture from the elastomer, it appreciably worsens its resilience properties as a result of the considerable mechanical stress to which it is subjected.